1. Field of the Invention
This invention relates to an apparatus and method for simultaneous laser machining of defined patterns on the surface of a workpiece.
2. Description of Related Art
Lasers are used for a variety of materials machining purposes including drilling, contouring surfaces, cutting, scribing, trimming and pattern depositions. Typically, carbon dioxide lasers are used for scribing, drilling and machining. Excimer lasers are used for film ablation, flex circuits and relief cutting. YAG lasers are used for trimming resistors, capacitors, marking and cutting of metals, semiconductors and absorptive synthetics. An apparatus and method for sequentially drilling small holes in a workpiece using a laser are described by LaPlante et. al in U.S. Pat. No. 5,168,454. Orienting and focusing a single laser beam to scan a workpiece using such a method is slow and inefficient compared to parallel processing using multiple laser beams.
In the past, the creation of a plurality of beamlets for laser machining has been dependent on external beam shaping optics and deflecting devices to machine different points on a workpiece simultaneously. Typically, optical interface, scattering and transmission losses reduce system efficiency, requiring increased energy from the laser. Further, the use of a separate deflecting device not only increases system complexity but also increases the optical path length and required alignment precision.
In U.S. Pat. No. 5,676,866, Baumen et al. describes a microlens optical element which divides a laser beam into a plurality of beamlets which in turn are deflected by separate independent mirrors. This arrangement permits the simultaneous machining of a workpiece, e.g., the drilling of multiple holes. The position of the individual beams can be rapidly displaced in their coordinate location or with sufficient mirror deflection, removed from the optical path. The complexity and optical inefficiency of this system adds significant structure and cost.
In U.S. Pat. No. 6,037,564, Tatah describes a diffractive element which diffracts a single laser beam into a plurality of beamlets that are in turn deflected by individual micromirrors so as to simultaneously machine a workpiece. The micromirrors are two state devices either directing the beamlets to the workpiece or away from it. Galvo mirrors are used to displace the beamlets in their coordinate position. The complexity and optical inefficiency of this system adds significantly more structure and cost when compare to the Baumen et. al. technique described above.
Other laser machining devices such as described in U.S. Pat. Nos. 5,268,554 and 5,113,055 have the disadvantages of sequential scanning and changing beam size with deflection.
In U.S. Pat. No. 5,864,430, Dickey et al. discloses a laser with a Gaussian beam profile which is modified to produce a beam with a uniform profile using the Fourier transform properties of lenses. Complex optical elements, including a telescope to control the beam radius, transform lenses to set the target spot and focal length. Phase elements are required to determine the quality of the system. The system is complex and requires precision alignment, which adds to its cost. Further, physical elements must be changed to change beam characteristics.
Other beam shaping systems such as described in U.S. Pat. Nos. 5,925,271, 5,848,091 and 4,744,615 use fixed optical elements external to the laser to shape the beam profile. Optical interface, scattering and transmission losses reduce system efficiency requiring increased energy from the laser resulting in cost and complexity disadvantages.
It is clear from the foregoing analysis that a serious need exists for a laser machining apparatus which avoids the problem of non-uniform laser beam profiles which results from multimode oscillations in the laser cavity, and which allows for the creation of multiple beamlets from a single laser beam for rapid material machining. Prior art solutions use external optical elements and mirrors to solve both of these problems resulting in complex structures, optical inefficiency, precision alignment and significant added cost.
Briefly described, the invention comprises a laser apparatus for simultaneous machining at several points on the surface of a workpiece. The apparatus includes a laser laser cavity containing a first micromirror array having a first plurality of individual micromirrors for generating a patterned beam of discrete laser beamlets from a single laser beam. The apparatus also includes a second micromirror array having a second plurality of individual micromirrors for modifying the patterned plurality of laser beamlets and deflecting them onto several points on the surface of a workpiece. Also included in the apparatus are means for controlling each of the micromirrors of both micromirror arrays so that each is changeable in position independently of each other. When the individual micromirrors of the second array are positioned to reflect laser beamlets of equal energy distribution, a two-dimentional pattern is produced on the surface of the workpiece. Alternatively, when the individual micromirrors of the second array are positioned to reflect laser beamlets of unequal energy distribution, a three-dimentional pattern is produced on the surface of the workpiece.
The invention may be more fully understood by reference to the following drawings.